Boletus edulis — King bolete, cep, Steinpilz, penny bun

Card image cap

King bolete1,3, photograph by Paul Kroeger.

Edible

Gills: None, small white or yellowish pores
Spore print: Olive brown

Left image: King bolete3, photograph by Paul Kroeger.
Right image: Net-like 'reticulum' on stem, photograph by Paul Kroeger.


Odour: Mild, pleasantly mushroomy.
Cap: 5–30 cm in diameter. Caps hemispherical when young, expanding with age to become flattened or somewhat wavy around the edges. The colour varies from pale beige to tan to reddish brown. Surface may be dry or wet/slimy if weather is moist. Often partly buried in duff, looking like a bakery bun emerging from leaf litter.
Pores: On the underside of the cap find pores or minute holes (look closely, they are only ~0.3–0.5 mm wide7). Pore surface is white when young and pores are stuffed with whitish cottony tissue; pores open and become yellowish with age. Pore colour does not change to blue or brown after being rubbed (check ~10 min after rubbing).
Stems: (3) 8–25 cm long x 1.5–2.5 cm wide near the cap; up to 12 cm wide at the base, bulbous when young, later more cylindrical, often with a tapering or pointed base. The abruptly bulbous base in the photo above is unusual. Surface white when young, to tan or pinkish coloured in upper half with age. Look closely for the pale, net-like pattern (‘reticulum’, see insert in image above) at the top of the stem. Flesh in cap and stem white and firm.
Ring or veil: None.
Cup: None.
Spores: 13–18 x 4–7 µm, olive brown, without a germ pore.
Habitat: In small groups on the ground, often partly buried under leaf litter. In the Pacific northwest, often in hemlock (Tsuga heterophylla), spruce (Picea sitchensis), pine (Pinus spp.) and fir (Abies spp.) forests1,2 but with oaks (Quercus spp.) and other broad-leaved trees in Europe8.
Geographic distribution: Widely distributed across North America and Europe.

Rule out poisonous species before eating a mushroom with a 'bakery bun' shape. First look closely at the underside of the cap; in king boletes, this surface is always covered with tiny pores. Poisonous Cortinarius species with a similar shape and colour will have radiating, linear gills rather than pores. Check that the top third of the stem is covered by a reticulum: white, net-like raised ridges just visible with the naked eye (see 'Additional images'). Boletus edulis has light tan to yellowish pores, and pores and stem do not become blue where rubbed. Several poisonous species including Rubroboletus eastwoodiae and Neoboletus erythropus are similar BUT they have orange or red pores that usually change to blue/black within ~10 min of being rubbed. Boletus edulis is not bitter tasting; bitter-tasting boletes are considered inedible.

Other edible species that look like the king bolete include the spring king, Boletus rex-veris that fruits in spring, after the morel season6. Xerocomellus zelleri (=Boletus zelleri, Zeller's bolete) and the western cracked cap bolete (ours is probably an undescribed species9 but is variously called Xerocomellus chrysenteron or Boletus chrysenteron) are common in late summer and fall in cities and forests. Zeller's bolete has a smooth, brownish to black cap, yellow pore surface that bruises blue, and at least some red colour on the stem. Colours of the cracked cap bolete are similar, but as its name suggests, its cap surface is usually cracked.

King boletes are edible for most people. A rare few individuals get sick from them with upset stomachs, vomiting, and diarrhoea.

Treatment: Contact your regional Poison Control Centre if you or someone you know is ill after eating boletes. Poison centres provide free, expert medical advice 24 hours a day, seven days a week. If possible, save the mushrooms or some of the leftover food containing the mushrooms to help confirm identification.

Poison Control:
British Columbia: 604-682-5050 or 1-800-567-8911.
United States (WA, OR, ID): 1-800-222-1222.

1
UBC. University of British Columbia Herbarium Database, <http://bridge.botany.ubc.ca/herbarium/database.php> accessed February 1, 2018.
2
DAVFP. Pacific Forestry Centre's Forest Pathology Herbarium, Collections Database, <http://cfs.nrcan.gc.ca/herbarium> accessed February 1, 2018.
3
Specimen Boletus edulis UBC F32159, GenBank #MF955211.
4
Scates, K. Trial field key to the boletes in the Pacific Northwest, <http://www.svims.ca/council/Bolete.htm> accessed June 10, 2017.
5
Arora, D. Mushrooms Demystified. Ten Speed Press, Berkeley, California (1986).
6
Arora, D. California porcini: three new taxa, observations on their harvest, and the tragedy of no commons. Econ. Bot. 62, 356-375, doi:10.1007/s12231-008-9050-7 (2008).
7
Smith, A. H. & Thiers., H. D. The Boletes of Michigan. University of Michigan Press, Ann Arbor, Michigan (1971).
8
Abarenkov, K. et al. PlutoF-a Web based workbench for ecological and taxonomic research, with an online implementation for fungal ITS sequences. Evol. Bioinf. 6, 189-196, doi:10.4137/ebo.s6271 (2010).
9
Siegel, N. & Schwarz, C. Mushrooms of the Redwood Coast. A Comprehensive Guide to the Fungi of Coastal Northern California. Ten Speed Press, Berkeley, California (2016).